Key Engineering Materials Vols. 348-349

Abstract: Sliding polymer-polymer surface contacts, due to their inherent elastic properties, exhibit detachment waves also termed as Schallamach waves. Such waves effect the initiation and propagation of wear along the sliding contacts. This paper presents quasi steady-state analysis of such a sliding contact using finite element. The contact is modeled and nodal solutions for pressure are obtained for small sliding steps. Analysis of orthogonal pressure components at the contact nodes reveals the formation of Schallamach wave phenomenon. Further, appropriate wear law is used for calculation of wear at nodal level.

Abstract: Considering the aerospace structures, the advantages of Al-Li alloys in comparison with conventional aluminium alloys comprise relatively low densities, high elastic modulus, excellent fatigue and toughness properties, and superior fatigue crack growth resistance. Unfortunately, these alloys have some disadvantages due to highly anisotropic mechanical properties and due to a very high crack growth rate for microstructurally short cracks. This could mean relatively early cracking in high stress regions such as rivet holes in helicopter fuselage panels. Consequently a more accurate approach in fatigue life analysis is requested. Considering that the 8090 T81 aluminium alloy has been widely used in an helicopter structure, in particular in the bolted connection between the stringers and the modular joint frame in the rear of the fuselage, it is extremely important to found a reliable procedure for the fatigue life assessment of the component. Thus, using the results of experimental tests made on panel specimens, a FE general model and two submodels of the critical zone (involved in fatigue damage during the tests) have been modelled in order to investigate the complex state of stress near the rivets holes. These stress values obtained have been elaborated for a fatigue assessment.

Abstract: An experimental investigation was conducted to study the seismic behavior of slabcolumn connections under vertical shear and cyclic lateral load. Test variables include gravity shear ratio (V /V0 g ) and flexural reinforcement ratio (ρ ) of slab within an effective slab width between lines that are one and one-half slab thickness ( c 3h 2 + ). The strength and ductility of the test specimens were evaluated in accordance with gravity shear ratios and slab reinforcement ratios. The shear strength of the test slabs was compared with the predictions by ACI 318-05.

Abstract: The impact testing is an efficient experimental method that enables the quantitative and qualitative determination of the fatigue resistance of mono- and multilayer coatings deposited on various substrates, which was not possible with the common testing methods previously available. In this paper the experimental assessment of the fatigue resistance of coatings working under cyclic loading conditions by means of the dynamic impact testing method is presented. The fatigue failure mode, such cohesive or adhesive, of the investigated coatings is determined using scanning electron and optical microscopy, as well as EDX analysis. Critical values of the stress components, responsible for distinctive fatigue failure modes of the coating substrate system are obtained and the fatigue limits of aluminide coatings are illustrated in simple diagrams containing the impact load versus the number of successive impacts that the examined aluminide-P91 system can withstand.

Abstract: The constant-ductility seismic demand spectra can provide high-sight of seismic damage mechanism of inelastic structures under the earthquake. And in the displacement-based seismic design, the constant-ductility seismic demand spectra are very useful for the preliminary design of new structures where the global displacement ductility capacity is known, which can provide the required inelastic lateral strength of new structures from the required elastic lateral strength. An in-depth investigation of damping effect on constant-ductility seismic demand spectra of inelastic structures is presented in this paper. A statistical study is performed of inelastic response computed for different damping ratio SDOF systems with different levels of lateral yielding strength required to maintain the given displacement ductility when subjected to a large number earthquake accelerations. It is concluded that the damping effect on constant-ductility seismic resistance spectra is rather complex. It depends on not only site conditions but also the structural period. Finally, results from non-linear regression analysis are presented that provide a simplified expression to be used to approximately quantify the damping effect.

Abstract: Fattiigue and ttensiille properttiies of speciimens cutt from palllletts made from wastte pllasttiics by usiing of newlly develloped recyclliing apparattus are presentted.. Testted matteriialls are pollypropyllene fiillm,, pollypropyllene pelllletts,, pollyetthyllene,, pollyetthyllene-20wtt%flly ash composiitte and pollyetthyllene -20wtt% callciium carbonatte composiitte.. Itt can be conclluded tthatt tthe newlly develloped recyclliing apparattus make possiiblle tto proviide palllletts made from wastte pollypropyllene and pollyetthyllene wiitth ullttiimatte ttensiille sttrengtths of more tthan niinetty percentt of tthose made from fresh pollypropyllene and pollyetthyllene.. Itt has become cllear tthatt carefull ttreattmentt of composiitte process for wastte pllasttiics enablle tto iimprove fattiigue sttrengtth of pollyetthyllene composiittes by sttrengttheniing tthe iintterface bettween an addiittiive and base matteriiall..

Abstract: The optimization is the process of searching for the best results in a certain load case. Complete definition of optimization includes three conditions, which are closely connected: • optimization target, defined with object function, • subject of optimization, • optimization methods. The object functions can be different process parameters such as costs, manufacturing time, costefficiency, productivity etc. In designing of the structures such as a crane there is a tendency particularly towards reducing the weight of steel structures with the same load-carrying capacity. Thus the object function can be the volume, weight or mass of the structure. In the paper we will devote ourselves to optimization of truss structures-gantry crane mean girder by means of the FEM. This method has become indispensable in all areas of analyses of structures in combination with mathematical modeling and mathematical methods of optimization and is particularly of assistance to designers in conceiving the steel structures.

Abstract: In this paper the energy absorption of thin-walled aluminium tubes used as crash boxes in the body structure of a vehicle has been optimized. In order to achieve this, various cross-sections of extruded aluminium were chosen and their behaviour under dynamic impact loading was investigated. The crash boxes were made from aluminium alloy 6060 temper T4. Finite element software LS-DYNA in ANSYS was used for modelling. For each cross-section, the results of dynamic crushing load versus crushing distance was obtained from the FE simulation and the results were compared with the experimental and numerical work on a square crash box in the literature. Parameters such as the crush force efficiency and the specific energy of various crash boxes were compared with the relevant ones for the square crash box and the most efficient crash box was recommended.

Abstract: In the last years there has been an increasing interest in the multi-scale mechanics of the materials, i.e. in predicting the macroscopic constitutive response on the basis of the underlying microstructure. At each level of structural hierarchy, one may model the material as a continuum, and the representative volume element problem can be formulated in terms of standard equilibrium and boundary conditions. The overall physical behaviour of these micro-heterogeneous materials depends strongly on the shape, size, orientation, properties and spatial distribution of their microconstituents. For prediction of the macroscopic behaviour of such materials the multi-scale homogenization techniques were developed. As an example of such investigation we develop the hierarchical material model of the chemical vapour infiltrated carbon fiber composites (CFCs) with a unidirectional or random distribution of fibers. The approach based on hierarchical structural modeling can be used to theoretically predict the mechanical parameters of CFCs with different microstructure and to develop virtual materials with prescribed mechanical properties.